Plants are subject to a wide variety of fungal and bacterial diseases and damage by insects. Fruit bearing plants, in particular citrus trees are subject several totally destructive diseases, Xanthomonas axonopodis pv. Citri (Xac), Asiatic citrus canker (Canker) and Huanglongbing/Citrus Greening (Liberibacter asiaticus(CGD), which is vectored by the Asian citrus psyllid (AsCP), Diaphorina citri Kuwayama (Greening).
Citrus canker and Greening are particular problems for citrus crops as is the insect vector, psyllids. Presently, Greening is prevalent worldwide throughout all the countries that produce citrus; there is no known cure. The official, sometimes mandated, scientific worldwide recommendation is for trees identified and affected with Greening to be removed and burned. In the case of Canker, hundreds of thousands of acres worldwide have been destroyed and removed because of the effects of the disease. Presently the only official recommendation by the scientific community, is prophylactic by spraying surface protectents on the plant tissue of citrus trees, which has little or no effect because these surficial fungicidal sprays are easily washed off by moisture.
It would be desirable to have products that can be applied to fruit bearing plants that will systemically stop or effectively retard damage caused by fungal and bacterial diseases and insects while at the same time also fertilizing these plants and allowing the plants to rejuvenate while being healed and then continue to bear fruit, preferably in increased yields.
A one product “weed and feed” technology has long been available in the turf industry as a superior method to control weeds and promote plant growth; doing two jobs simultaneously and saving the cost of separate applications. If just a nutrient was applied separately to weed infested turf, both the turf and the weeds would benefit more than the turf. Likewise, if a costly second herbicide application was made applied separately the target weeds would be controlled but the grass would not grow quickly enough to outgrow the next crop of weeds.
Phosphorus (P) is one of the major elements required by all living species to grow and develop. When the element phosphorus is oxidized to the fullest extent possible, its acid is termed phosphoric acid, [H3PO4 or PO(OH)3], and the salts of phosphoric acid are termed phosphates, e.g. K2HPO4. With phosphorus in a slightly less oxidized form, the phosphorus in the acid form is termed phosphorous acid, [H3PO3, or HPO(OH)2], and the salts of phosphorous acid are termed phosphites, e.g. K2HPO3. Phosphites are marketed either as an agricultural fungicide, bactericide or without research data as a superior source of plant phosphorus (P) nutrition.
Polyphosphates are sometimes referred to as pyrophosphates. Additional phosphate ions may react further with the polyphosphate, P2O7−4, to form longer polyphosphates and, in general, there is a mixture of varying polymer chain lengths in any given sample. The presence of some proportion of polyphosphates in a fertilizer is useful for purposes of sequestration of impurities, as suspensions aids, and for making phosphorus more available to plants.
On the other hand, the lower valent phosphite, (PO3−3), has never played an important role in the commercial fertilizer industry.
The analysis of polyphosphite content in a composition is difficult because all common wet chemical methods for determination of phosphite depend upon reagents that first convert phosphite to phosphate. These reagents will break up any polyphosphite molecules present in the composition into individual phosphite ions. Polyphosphite, therefore, cannot be detected or quantified by the routine wet chemical methods. For instance, iodine solutions are used to oxidize inorganic phosphites for subsequent analysis as phosphate. Iodine will breakup any phosphite polymer present and the polyphosphite will not be detected. Similarly, commercial labs which analyze fertilizers do not report phosphite levels but rather report them as phosphate. Also, during analytical procedures requiring heat, phosphites would typically be slowly converted to phosphate unless precautions are taken to prevent oxidation by excluding air. Furthermore, at elevated temperatures polyphosphites can be expected to hydrolyze to ordinary phosphite ion, analogously to the hydrolysis of polyphosphates under similar conditions. Accordingly, physical methods such as nuclear magnetic resonance (NMR), high pressure liquid chromatography (HPLC), liquid chromatography, mass spectrometry (MS), and other physical molecular weight determining methods are useful methods for characterizing polyphosphites.
NMR provides a unique method of detecting phosphite because in most cases, and particularly when in solution, it exists with a hydrogen attached to the phosphorus atom (HPO3−2). Sophisticated NMR instruments, such as the Varian VXR-3005 spectrometer, can not only detect and measure P.sup.31 but can also simultaneously perform measurements on atoms such as hydrogen attached to phosphorus or carbon by transfer polarization. Such an instrument can, therefore, detect and measure phosphite in the presence of other phosphorus species without ambiguity.
Potassium phosphite would be particularly useful because it would provide the second important nutrient of the three critical plant nutrients, potassium. Moreover, a polyphosphite can be expected to provide the sequestration and slow release advantages known with polyphosphate, although phosphites are more active fungicides.
Phosphites are highly selective, non-toxic fungicides active against numerous fungal pathogens, and provide both protective and curative responses against such plant disease isolates of Phytophthora, Rhizoctonia, Pythium, and Fusarium, and other plant diseases—but typically not against bacterial diseases. Additional information regarding phosphorus-based fertilizers is presented in the “Background of the Invention” section of U.S. Pat. No. 7,887,616, the contents of which are hereby incorporated by reference.
Current commercial methods for making salt compositions from phosphoric acid and phosphorous acid (Phosphorus (P) acids), for foliar application to plants are described in the “Background of the Invention” section of U.S. Pat. No. 8,193,119, the contents of which are hereby incorporated by reference.